Cats leave about 1.2 million metric tons of feces in the environment yearly in the United States alone. Some of that waste contains an infectious parasite called Toxoplasma gondii, which has recently caused toxoplasmosis epidemics in otherwise healthy people, not only in pregnant women or people with weakened immune systems.

Women newly infected during pregnancy can pass the toxoplasmosis infection to unborn children with possible severe consequences such as diseases of the eyes and nervous system, according to the U.S. Centers for Disease Control and Prevention.

Research has also linked T. gondii to schizophrenia, obsessive-compulsive disorder, rheumatoid arthritis, brain cancer and even children having trouble in school, according to the article, which was published in the July 9 issue of the journal Trends in Parasitology.

"The accumulation of Toxoplasma gondii oocysts, found in cat feces, may be a much bigger problem than we realize because of their apparent long life and their association with some diseases," said E. Fuller Torrey, director of the Stanley Medical Research Institute.

Research has shown that backyards and communities may contain more than 400 oocysts per square foot in places where cats frequently leave feces, according to a journal news release. Even a single oocyst can cause an infection.

Cats typically become infected when they eat infected birds, mice or other small animals. Torrey called for better control of outdoor cats. There is little need to worry about indoor cats, he said.

The researchers offered some prevention advice. If your cat or a neighbor's cat spends time outdoors, take care with litter boxes, keep sandboxes covered and wear gloves when gardening. Dirt under your fingernails could contain up to 100 T. gondii oocysts, according to one estimate. Be extra careful if you have young children.

Other than pregnant women, people shouldn't bother getting tested, Torrey said. Fifteen percent of people have antibodies and someone who tests positive at one point can later test negative.